Wideband transmitter front-end

ABSTRACT

One embodiment of the present invention provides a transmitter for wireless communication. The transmitter includes a wideband tunable modulator, a number of power amplifiers with a particular power amplifier associated with a particular frequency range, and a wideband power amplifier (PA) driver. The PA driver is configured to receive an output signal from the wideband tunable modulator, amplify the output signal, and send the amplified output signal to at least one of the power amplifiers.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/363,056, entitled “WIDEBAND TRANSMITTER FRONT-END,” by inventors ShihHsiung Mo, Yan Cui, and Chung-Hsing Chang, filed 31 Jan. 2012, whichclaims the benefit of U.S. Provisional Application No. 61/526,853,entitled “Wideband Transmitter Front-End,” by inventors Shih Hsiung Mo,Yan Cui, and Chung-Hsing Chang, filed 24 Aug. 2011.

BACKGROUND

1. Field

The present disclosure relates generally to the transmitter front-end ofa wireless communication system. More specifically, the presentdisclosure relates to a novel low-power wideband transmitter front-end.

2. Related Art

Traditional wireless communication systems are usually designed for aspecific standard, such as GSM (Global System for Mobile Communications)or Wideband Code Division Multiple Access (W-CDMA), each requiringdifferent carrier frequencies. For example, the carrier frequency of theGSM signals varies from 800 MHz to 1 Ghz, while the carrier frequency ofthe W-CDMA signals varies between 2-3 GHz. Current demand for theconvergence of wireless services, in which users can access differentstandards from the same wireless device, is driving the development ofmulti-standard and multi-band transceivers, which are capable oftransmitting/receiving radio signals in the entire wirelesscommunication spectrum (from 300 MHz to 3 GHz).

To meet multi-standard and multi-band requirements, the RF front-end(which includes circuitry between the antenna and the first intermediatefrequency (IF) stage) needs to operate over a frequency range coveringthe entire wireless communication spectrum.

SUMMARY

One embodiment of the present invention provides a transmitter forwireless communication. The transmitter includes a wideband tunablemodulator, a number of power amplifiers with a particular poweramplifier associated with a particular frequency range, and a widebandpower amplifier (PA) driver. The PA driver is configured to receive anoutput signal from the wideband tunable modulator, amplify the outputsignal, and send the amplified output signal to at least one of thepower amplifiers.

In a variation on this embodiment, the transmitter further includes asingle-pole multiple-throw switch situated between the wideband PAdriver and the power amplifiers. The switch is configured to switch theamplified output signal to one of the power amplifiers based on acarrier frequency of the output signal.

In a variation on this embodiment, the wideband tunable modulator andthe power amplifier are located on a same integrated circuit (IC) chip.

In a variation on this embodiment, the wideband tunable modulator is aquadrature modulator.

In a variation on this embodiment, the wideband tunable modulator has atuning range between 300 MHz and 3.6 GHz.

In a further variation, the wideband tunable modulator includes anamplifier. The bandwidth of the amplifier is compensated for by using aninductive peaking technique.

In a variation on this embodiment, the wideband PA driver includes acascode amplifier.

In a further embodiment, the cascode amplifier has two poles.

In a further embodiment, the cascode amplifier includes an inductor thatis serially coupled to a parasitic capacitor.

In a further embodiment, the inductor has an inductance between 0.5 nHand 10 nH.

In a variation on this embodiment, the wideband PA driver has a 10 dBbandwidth that is up to 3.6 GHz.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 presents a diagram illustrating the architecture of aconventional wireless transmitter (prior art).

FIG. 2 presents a diagram illustrating the architecture of a wirelesstransmitter, in accordance with an embodiment of the present invention.

FIG. 3A presents a schematic of a conventional mixer (prior art).

FIG. 3B presents a schematic of a mixer, in accordance with anembodiment of the present invention.

FIG. 4A presents a schematic of a conventional power amplifier (PA)driver (prior art).

FIG. 4B presents a diagram illustrating an exemplary frequency responseof the return loss for a conventional PA driver (prior art).

FIG. 4C presents a schematic of a wideband power amplifier (PA) driver,in accordance with an embodiment of the present invention.

FIG. 4D presents a diagram illustrating an exemplary frequency responseof the return loss for a wideband PA driver, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

Overview

Embodiments of the present invention provide a solution for a low-powertransmitter front-end. In one embodiment, the transmitter chip includesa wideband power-amplifier driver that is capable of amplifying RF(radio frequency) signals over a wide frequency range.

Wideband Transmitter Front-End

FIG. 1 presents a diagram illustrating the architecture of aconventional wireless transmitter (prior art). Transmitter 100 includesa baseband signal processor 102, a digital-to-analog converter (DAC)104, a low-pass filter (LPF) 106, a number of quadrature modulators(such as modulator 108), a number of power-amplifier (PA) drivers (suchas PA driver 110), a number of PAs (such as PA 112), an n×1 switch 114,and an antenna 116.

During operation, baseband signals provided by baseband signal processor102 are converted from the digital domain to the analog domain by DAC104. LPF 106 filters out any out-of-band noise. Modulators operating atdifferent frequencies modulate the baseband signal at differentfrequency bands. The output of a particular modulator, thus RF signal ata particular carrier frequency, is sent to a dedicated PA driveroperating at that carrier frequency. For example, the output ofmodulator 108 is sent to PA driver 110, which is optimized to work atthe operating frequency of modulator 108. The output of a PA driver isthen sent to a corresponding PA (often located off-chip), which is alsooptimized to work at the same frequency band. Note that a PA driverneeds to be able to deliver a considerable power to its correspondingPA, which has a 50 Ohm input impedance. For example, the output of PAdriver 110 is sent to PA 112. Depending on the currently active standardor mode of operation, n×1 switch 114 selects the output of a desired PA,thus RF signal at the desired carrier frequency, and sends the RF signalto antenna 116 for transmission.

Note that, as shown in FIG. 1, the PA drivers (such as PA driver 110),the modulators (such as modulator 108) and LPF 106 are often integratedonto a single integrated circuit (IC) chip 118. With a dedicatedmodulator and a dedicated PA driver for each frequency band, thetransmitter performance can be optimized for each frequency band.However, a large amount of chip area is required to accommodate themultiple PA drivers and modulators. In addition, a large number ofinput/output lines will be needed, which not only increases the chipsize, but also the size of a supporting printed circuit board (PCB),thus significantly increasing the size of the packaged device.

To reduce the size of the transmitter chip and the supporting PCB, it isdesirable to use a single modulator and a single PA driver for themultiple frequency bands. FIG. 2 presents a diagram illustrating thearchitecture of a wireless transmitter, in accordance with an embodimentof the present invention. In FIG. 2, transmitter 200 includes a basebandsignal processor 202, a DAC 204, a low-pass filter (LPF) 206, a tunablequadrature modulator 208, a wideband PA driver 210, a number of PAs(such as PA 214), a 1×n switch 216, an n×1 switch 218, and an antenna222.

LPF 206, tunable modulator 208, and wideband PA driver 210 formtransmitter chip 212, which has far fewer I/O lines than conventionaltransmitter chip 118. A 1×n switch 216, an n×1 switch 218, and themultiple PAs form a PA chip 220. 1×n switch 216 ensures that RF signalsof a particular frequency band are sent to a corresponding narrowbandPA, and n×1 switch 218 ensures that the output of the different PAs aresent to antenna 222 via a single input.

To enable multi-standard/multi-band application, tunable modulator 208and wideband PA driver 210 need to have a bandwidth covering the entirewireless communication bandwidth, which is from 300 MHz all the way to3.6 GHz. Hence, the tuning range of tunable modulator 208 needs to bebetween 300 MHz and 3.6 GHz. Such a wide bandwidth imposes a number ofdesign challenges, especially for wideband PA drivers, which have alarge dynamic range. On the other hand, the gain requirement for a mixerused inside a typical modulator is relatively low, making designing themodulator less difficult. In one embodiment, an inductive peakingtechnique is used to increase the bandwidth of an amplifier used in themixer.

FIG. 3A presents a schematic of a conventional amplifier used for amixer (prior art). In FIG. 3A, amplifier 300 includes a transistor 302and a resistor 306. Note that a capacitor 304 in FIG. 3A is theparasitic capacitance. An exemplary resistance of resistor 306 is 50Ohm, and an exemplary capacitance of parasitic capacitor 304 is 800 fF.The bandwidth of amplifier 300 is limited by the existence of parasiticcapacitor 304. More specifically, the gain curve of amplifier 300 dipsat higher frequencies.

FIG. 3B presents a schematic of an amplifier in accordance with anembodiment of the present invention. Amplifier 320 has a similarstructure compared with amplifier 300 except that amplifier 320 includesan additional inductor 308 situated between resistor 306 and the powersupply. In one embodiment, the inductance of inductor 308 is 12 nH. Notethat at lower frequencies, inductor 308 has minimum impact, and athigher frequencies (such as in the GHz range), inductor 308 resonateswith parasitic capacitor 304, thus increasing the bandwidth of amplifier320. In one embodiment, the bandwidth of amplifier 320 expands beyond 3GHz.

Due to the large dynamic range of PA driver, inductive peaking is nolonger an optimum solution for increasing the bandwidth of the PA driverbecause the resistance load (resistor 306) introduces voltage drop. Inone embodiment, a double-pole solution is used to increase the bandwidthof an amplifier, such as an operational amplifier.

FIG. 4A presents a schematic of a conventional power amplifier (PA)driver (prior art). PA driver 400 includes a pair of transistors 402 and404, and an inductor 406. Transistors 402 and 404 form a cascodeamplifier. The bandwidth of PA driver 400 is limited by parasiticeffects. More specifically, parasitic capacitors resonate with inductor406, causing the input return loss (the S₁₁ parameter) frequencyresponse curve to dip at the resonance frequency (or the pole location).FIG. 4B presents a diagram illustrating an exemplary frequency responseof the return loss for a conventional PA driver (prior art).

FIG. 4C presents a schematic of a wideband power amplifier (PA) driver,in accordance with an embodiment of the present invention. Similarly toconventional PA driver 400, wideband PA driver 420 includes a cascodeamplifier (transistors 422 and 424), a parasitic capacitor 430, and achoke inductor 428. Note that parasitic capacitor 430 may include anadditional parallel capacitor. In addition, wideband PA driver 420includes a serial inductor 426, a parallel capacitor 432, and a DC-blockcapacitor 434. Serial inductor 426 is situated between parasiticcapacitor 430 and parallel capacitor 432, as shown in FIG. 4C. In oneembodiment, parallel capacitor 432 is coupled to an output bond pad 436,and choke inductor 428 is located off-chip.

The added serial LC increases the bandwidth of wideband PA driver 420because now there are two resonance frequencies (two poles),corresponding to two dips in the return loss frequency response curve.FIG. 4D presents a diagram illustrating an exemplary frequency responseof the return loss for a wideband PA driver in response to an embodimentof the present invention. As one can see from FIG. 3D, the existence ofthe two poles (one at f₀ and another one at f₁) significantly increasesthe bandwidth of PA driver 420. In one embodiment, the bandwidth of thetwo-pole amplifier is 20% more than that of the conventional amplifier.By carefully selecting the values of inductors 426 and 428, oncommunication frequency range (up to 3.6 GHz). In one embodiment, theinductance of inductor 426 is between 0.5 nH and 10 nH, and theinductance of inductor 428 equals or is greater than 33 nH.

The wideband PA driver and wideband mixer allow the transmitter chipmanufacturer to manufacture the same type of transmitter chips that canbe sold to different markets where different standards are implemented,thus significantly reducing the designing and manufacturing cost.

The foregoing descriptions of embodiments of the present invention havebeen presented only for purposes of illustration and description. Theyare not intended to be exhaustive or to limit this disclosure.Accordingly, many modifications and variations will be apparent topractitioners skilled in the art. The scope of the present invention isdefined by the appended claims.

What is claimed is:
 1. A transmitter for wireless communication,comprising: a single wideband tunable modulator having tuning range from300 MHz all the way up to 3.6 GHz; a number of power amplifiers, whereina particular power amplifier is associated with a particular frequencyband; and a single wideband power amplifier (PA) driver coupled to thesingle wideband tunable modulator and the power amplifiers, wherein thesingle wideband PA driver is coupled to the power amplifiers via aband-selection switch, and wherein the single wideband PA driver isconfigured to: receive an output signal from the wideband tunablemodulator, wherein a frequency of the output signal is between 300 MHzand 3.6 GHz; amplify the output signal; and send the amplified outputsignal to at least one of the power amplifiers via the band-selectionswitch.
 2. The transmitter of claim 1, further comprising a single-polemultiple-throw switch situated between the wideband PA driver and thepower amplifiers, wherein the switch is configured to switch theamplified output signal to one of the power amplifiers based on acarrier frequency of the output signal.
 3. The transmitter of claim 1,wherein the wideband tunable modulator and the power amplifiers arelocated on a same integrated circuit (IC) chip.
 4. The transmitter ofclaim 1, wherein the wideband tunable modulator is a quadraturemodulator.
 5. The transmitter of claim 1, wherein the single widebandtunable modulator includes an amplifier, wherein a bandwidth of theamplifier is compensated for by using an inductive peaking technique. 6.The transmitter of claim 1, wherein the wideband PA driver includes acascode amplifier.
 7. The transmitter of claim 6, wherein the cascodeamplifier has two poles.
 8. The transmitter of claim 7, wherein thecascode amplifier includes an inductor that is serially coupled to aparasitic capacitor.
 9. The transmitter of claim 8, wherein the inductorhas an inductance between 0.5 nH and 10 nH.
 10. The transmitter of claim1, wherein the single wideband PA driver has a 10 dB bandwidth that isup to 3.6 GHz.
 11. A method for generating a transmitter output forwireless communication, comprising: receiving a baseband signal;modulating the baseband signal onto an RF carrier, wherein the RFcarrier has a frequency that ranges from 300 MHz to 3.6 GHz;pre-amplifying the modulated signal using a single on-chip amplifierdriver regardless of the RF carrier frequency, wherein the singleon-chip amplifier driver is coupled to a group of power amplifiers via aband-selection switch; and sending the pre-amplified modulated signalvia the band-selection switch to a power amplifier selected from thegroup of power amplifiers based on the RF carrier frequency.
 12. Themethod of claim 11, wherein modulating the baseband signal is performedby an on-chip tunable modulator.
 13. The method of claim 12, wherein theon-chip tunable modulator includes an amplifier, wherein a bandwidth ofthe amplifier is compensated for by using an inductive peakingtechnique.
 14. The method of claim 13, wherein the amplifier is acascode amplifier.
 15. The method of claim 11, wherein modulating thebaseband signal involves quadrature modulating.
 16. The method of claim11, wherein pre-amplifying the modulated signal is performed by acascode amplifier.
 17. The method of claim 16, wherein the cascodeamplifier has two poles.
 18. The method of claim 17, wherein the cascodeamplifier includes an inductor that is serially coupled to a parasiticcapacitor.
 19. The method of claim 18, wherein the inductor has aninductance between 0.5 nH and 10 nH.